The present invention is directed to conveyors and, in particular, to a conveyor wherein a braking system is utilized to slow or stop an article moving along the conveyor, especially a roller conveyor.
In many types of conveyor systems, it is necessary to completely stop or at least slow articles passing along the system. This is particularly true of roller conveyor systems utilizing gravity to motivate pallets, packages or other articles along the conveyor. In the patent to Leemkuil U.S. Pat. No. 4,542,815, a system was described for providing such a brake. The Leemkuil system functions adequately in some installations, especially when the articles being transported along the conveyor are all of approximately the same weight and all have approximately the same velocity at the time they engage the braking system or retarder shown in Leemkuil.
However, when articles passing along the conveyor are of substantially different weights and/or have substantially different velocities, the Leemkuil structure may fail to bring the articles to consistantly the same velocity directly downstream of the retarder and may allow heavier articles to pass with little or no retardation. In particular, the release of the article in the Leemkuil system results from the bleeding of compressed air through a bleed valve directly associated with the actuator. Therefore, if a relatively heavy article directly engages the brake or engages and consequently tries to rotate a roller being held in position by such a brake, more pressure is exerted against the actuator than if a relatively light article makes the same engagement. Consequently, with a heavy article, the air in the actuator is urged through the bleed valve quicker and the braking mechanism is released faster. That is, for heavier articles, the delay time experienced because of the braking mechanism of Leemkuil is different than that of a lighter article.
As it was desirable to be able to completely stop or apply a continuous braking action for a predetermined amount of time in order to slow an article on a conveyor, especially a gravity roller type conveyor, it became desirable to develop a braking system in which the pressure within the actuator, resulting in a braking action, remained constant over a predetermined period of time and was not dependent upon the weight or velocity of articles being transported by the conveyor.